1. Field of the Invention
This invention is concerned with multilayer carrier films for supporting a fluid synthetic resin composition against a solid surface during curing of the resin.
2. The Prior Art
In the reconditioning of pipes, particularly sewer pipes laid below ground level, it is known to apply a layer of a liquid synthetic resin composition to the inner surface of the pipe and then to cure the resin to form an inert solid lining to the pipe. The resin is conveniently applied in the form of a fibrous mat which is impregnated with a curable resin composition and which is securely attached on one side to an impermeable carrier film. The resin composition-impregnated mat is placed next to the inner surface of the pipe with the carrier film on the outside and pressure is applied from the film side causing the mat to conform intimately with the surface. The resin is then cured. The fibrous mat serves as a reinforcing agent in the cured product.
In one known specific method of reconditioning a pipe, a mat of polyester fibres is secured face-to-face with a carrier film of polyvinyl chloride or of polyurethane. The latter may be formed in situ by melt coating. The combination is then converted into an elongated bag by stitching, and the joint and stitching are protected on the carrier film side by a patch of the same material as the carrier film, secured to the film surface by heat, a solvent or an adhesive. The mat is then impregnated with a composition consisting of an unsaturated polyester resin in a styrene base. The mouth of the bag, with the carrier film on the outside, is fixed to one end of the pipe and the closed end of the bag is pulled through the pipe so that the bag everts and the resin-impregnated mat lies next to the pipe wall, with the carrier film now on the inside of the bag. Hot water is then introduced under pressure into the inside of the bag for the purpose of pressing the mat against the pipe wall and for curing the resin.
In another method, as described in European Patent Publication No. 0168053, a polyester resin incorporating a light-activatable catalyst is used for the impregnation of a mat of acrylic or polypropylene fibres and the resin is cured when the assembly of impregnated mat and carrier film is within the pipe by exposing it to an appropriate light, for example ultra violet light. In this method it is necessary for the carrier film and the mat to permit the passage of the light to the resin to effect the curing.
In the operation of the above two methods it is necessary to impregnate the mat shortly before use and often on site, since during storage the resin composition rapidly attacks the polyvinyl chloride or polyurethene carrier film, causing it to become weakly attached to or even detached from the mat. Such a detachment could give rise to serious difficulties of application if detachment takes place before curing of the resin. A detachment after curing of the resin could cause serious obstruction problems, particularly if the pipe is below ground level. Impregnation of the mat on site is difficult and inconvenient.